The invention relates to filter units and a filter device for filtering a fluid in accordance with the preamble of claims 1 and 9. The invention further relates to a filtration process in accordance with the preamble of claim 11.
Gutman et al., U.S. Pat. No. 5,429,742 (=EP 508,645) discloses a filter composed of stackable filter units for filtering a fluid. The filter units are constructed as stackable disks which have a plastic frame and a filter medium which is molded into the plastic frame. By stacking together a plurality of filter units, an unfiltered channel for the fluid being filtered is formed, which is connected to the upstream sides of the filter units. The filter units furthermore form a filtered channel, which is connected to the downstream side of the filter units. To form a filter, the stacked filter units are provided with end plates, such that the first end plate has an aperture for the unfiltered fluid and the second end plate has an aperture for the filtered fluid. The disclosed filter uses dead-end filtration, that is to say 100% of the introduced unfiltered fluid must pass through the filter units and exit the filter through the filtered channel. Filtered material deposits on the filter elements and a filter cake forms on the filter units, which the fluid being filtered must penetrate. When the filter cake becomes thick enough, the filter becomes obstructed and flow through the filter becomes almost impossible.